Recently, polyester resins have been used as a material for components of a light emitting diode (LED). LEDs have rapidly replaced conventional light sources due to their excellent energy efficiency and long lifespan. Such an LED uses a polyester resin as a material for components such as a reflector, a reflector cup, a scrambler, and a housing.
An LED generally includes a light emitting semiconductor component, a wire, a housing, a reflector, and a transparent encapsulation member encapsulating the semiconductor component. Thereamong, the reflector can be formed of ceramics or heat resistant plastics. However, ceramics have poor productivity and heat resistant plastics suffer from deterioration in reflectance upon injection molding, heat-curing of an encapsulation member, or use under actual environmental conditions.
Conventionally, a polyphthalamide (PPA) resin, which is a heat resistant nylon resin having higher heat resistance than typical nylon resins, has mainly been used in a reflector for LEDs. However, such a heat resistant nylon resin suffers from significant degradation and color non-uniformity upon long term use of an LED, causing deterioration in performance of a product.
In order to overcome these problems, a modified polyester resin can be used instead of a PPA resin. Such a modified polyester resin is a polyester resin which includes glass fibers as a reinforcing agent and contains a benzene ring in a polyester backbone, and has higher heat resistance than typical polyester resins. Addition of a reinforcing agent can improve stiffness but also can reduce impact resistance. Thus, an additive for improving impact strength is commonly introduced. However, when such an additive is introduced into a typical polyester resin, the polyester resin can exhibit poor crystallinity, which can make injection molding at high temperature impossible or difficult.
Particularly, with design diversification and reduction in thickness of a reflector for LEDs, there is an urgent need for a polyester resin having improved impact strength so as to avoid brittleness during fabrication of an LED package. Japanese Patent Publication No. 1994-200132 A discloses a resin composition for lamp reflectors including a polyester resin and glass fibers; Japanese Patent No. 4,915,155 discloses a light reflective resin composition including an aromatic polycarbonate resin and a cycloaliphatic polyester resin; and Japanese Patent No. 4,325,753 discloses a light reflective polyester resin composition mainly composed of aliphatic polyester. However, these resin compositions cannot secure sufficient impact resistance or reliability of a reflector for LEDs.
Therefore, there is a need for a resin composition which can secure optical reliability while exhibiting excellent impact resistance and thus can be suitably used in an LED reflector.